Peer-Reviewed Publication
JMIR Med Inform2026;14e88390.September 11, 2026Journal Article

Privacy Leakage in Federated Learning in Radiology Reports: Comparative Evaluation of Tokenizer and Batch-Size Privacy Risks.

Santhosh Parampottupadam1,2, Andrés Martínez Mora1, Dimitrios Bounias1,2, Sinem Sav3, Klaus Maier-Hein1,2,4, Ralf Floca1
1Division of Medical Image Computing, German Cancer Research Center, Im Neuenheimer Feld 280, Heidelberg, Baden-Wurttemberg, 69120, Germany, 49 06221 420.
2Medical Faculty Heidelberg, Heidelberg University, Heidelberg, Germany.
3Department of Computer Engineering, Bilkent University, Ankara, Türkiye.
4Pattern Analysis and Learning Group, Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany.

Abstract

BACKGROUND: Federated learning (FL) enables multi-institutional model training on clinical text without sharing raw data; however, gradient inversion methods can reconstruct sensitive information from shared model updates. The extent of such privacy leakage in FL applied to radiology reports, and the role of tokenizer design, remains unclear. OBJECTIVE: This study aimed to quantify gradient-based…

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